Optimizing the predictive validity of NIRS kinetic profiles to predict aerobic capacity from a resting skeletal muscle occlusion test.

Measuring and monitoring individual cardiorespiratory fitness through a valid and accessible non-exhaustive surrogate is required. Techniques measuring haemodynamics have shown promise, and this study aimed to optimize the predictive validity of these approaches alongside developing predictive equations. In a two-study design, 8 (pilot study) and 30 (confirmation study) healthy adults completed exercise testing to assess maximal oxygen consumption ( ${\dot{V}}_{O_2\max }$ ) and an ischaemic occlusion test on the upper thigh to assess superficial femoral blood flow from ultrasonography and skeletal muscle oxygenation (SmO₂) by near-infrared spectroscopy (NIRS) before, during and post-cuff release. In study 1, treadmill running and a 5-min 220 mmHg ischaemic cuff pressure were performed, whereas in study 2, cycling ergometry and a 3-min 300 mmHg cuff pressure were applied. In study 1 and study 2, _abs ${\dot{V}}_{O_2\max }$ and _rel ${\dot{V}}_{O_2\max }$ were correlated to peak blood flow post-cuff occlusion (r = 0.57-0.84, all P < 0.01). In study 2, several NIRS based metrics of post-occlusive reactive hyperaemia were strongly correlated with _abs ${\dot{V}}_{O_2\max }$ and _rel ${\dot{V}}_{O_2\max }$ (all P < 0.001). Moreover, the magnitude of oxygen desaturation during the cuff occlusion was highly significantly related to both _abs ${\dot{V}}_{O_2\max }$ and _rel ${\dot{V}}_{O_2\max }$ (all P < 0.001). As an example, the SmO₂ desaturation slope was strongly associated with _abs ${\dot{V}}_{O_2\max }$ (r = -0.74, P < 0.001). Finally, intercorrelations between the rate of SmO₂ desaturation during cuff occlusion and the rate of SmO₂ reoxygenation and peak skeletal muscle blood flow post-cuff occlusion were observed (P < 0.01). An ischaemic-based test of skeletal muscle haemodynamic profiles could potentially be used to predict ${\dot{V}}_{O_2\max }$ and estimate a person's fitness.